Preamp RIAA

Modular HiFi Preamp

Andrew Martin, November 2025

This is a high quality modular HiFi Preamp largely based around circuits from Douglas Self.

The repo contains 4 main directories:

• KiCad_Main - the actual preamplifier
• KiCad_PSU - power supply for the preamplifier
• KiCad_RIAA - a separate RIAA preamplifier for MM cartridges
• KiCad_Switching - a relay-based switching board to allow up to 8 stereo inputs

KiCad_Main

The main preamplifier board is stereo and based very closely on the dual NE5532-based circuit in Self's Small Signal Amplifiers book.

KiCad_PSU

The PSU is a very standard design taking input from an 18-0-18V (AC) transformer and generating a regulated 17-0-17V (DC) output, plus a 12V DC output for the relays.

KiCad_RIAA

Again this is very closely based on the circuit from Douglas Self's Small Signal Amplifiers book, also published in Elektor. Many of the specified polystyrene capacitors now seem almost impossible to obtain (or are extremely expensive if you can find them) so I have substituted tight tolerance MLCC ceramic caps including one surface mount (as that seems to be the only form available in 1% tolerance).

Currently, only MM pickup cartridges are supported.

KiCad_Switching

The switching board is relay based and can be controlled by an 8-position rotary switch. 7 channels go through the main preamplifier, while the last takes the input from the RIAA preamp and doesn't use the main preamp. It carefully separates the 12V power for the relay coils from all the audio circuits.

You can, of course, use only some of the channels if you don't need so may inputs.

Other Directories

PDF Directory

The pdf directory contains PDFs of all circuit diagrams and PCB layouts.

BOM Directory

The bom directory contains BOMs for all the boards.

Images Directory

The images directory contains the images of the boards

ATTIC Directories

The ATTIC directories contain old versions before this project went under Git control.